Generally, for example, referring to U.S. Pat. No. 5,808,968 (JP-3221821-B2), an obstacle detection device for detecting an obstacle around a vehicle is provided with multiple ultrasound sensors which are arranged at a front bumper and a rear bumper of the vehicle. The ultrasound sensor is provided with ultrasound transmission-reception operation responding to one of multiple kinds of operation timing signals, each of which is repeated at a predetermined periodicity. Multiple detection areas around the vehicle are allotted to the ultrasound sensors. The ultrasound transmission-reception operation of the ultrasound sensor includes sending ultrasound burst to the detection area allotted thereto, and receiving ultrasound burst (reflection wave) reflected from the detection area.
In the case where there exists an obstacle in the detection area, the ultrasound sensor to which the detection area is allotted will receive the reflection wave reflected by the obstacle. Thus, the obstacle in this detection area can be detected, and an information operation is performed to inform the existence of the obstacle to a driver of the vehicle. The ultrasound sensor also receives signals other than the reflection wave, that is, noise. In order to eliminate the influence of noise, the information operation is performed when the ultrasound sensor continuously received the reflection wave for multiple times.
It is preferable to determine the detection of the obstacle as early as possible, while eliminating error information due to noise. Therefore, after the one ultrasound sensor commenced to receive the reflection wave, it is necessary for the one ultrasound sensor to perform the transmission-reception operation for the multiple times during the short time. On the other hand, the necessity for the ultrasound senor (other than the one ultrasound sensor) of the detection area where the obstacle detection has been determined to perform the transmission-reception operation during a short time becomes low, because the existence of the obstacle therein has been informed to the driver. In this case, it is preferable for the performance of the transmission-reception operation of the one ultrasound sensor which commenced to receive the reflection wave (that is, obstacle detection via the one detection unit is not determined yet) to have precedence over the other ultrasound sensor, which has received the reflection wave for the multiple times so that the obstacle detection has been determined. Thus, the obstacle detection via the one ultrasound sensor which commenced to receive the reflection wave can be early determined.
However, according to the obstacle detection device with reference to U.S. Pat. No. 5,808,968 (JP-3221821-B2), the ultrasound transmission-reception operations of the ultrasound sensors are performed at a predetermined periodicity regardless of development of determinations of the obstacle detections via the ultrasound sensors (that is, regardless of reflection-wave reception states of ultrasound sensors). Thus, it is difficult to early perform the detection of the obstacle in need of determination.